1. Field of the Invention
The present invention relates to navigation displays for use in aircraft navigation systems. More particularly, the invention relates to a navigation display that is driven by a stepper motor and a gear reduction mechanism.
2. Description of the Prior Art
Prior art avionics displays are typically driven by D'Arsonval movement. These types of displays include a pointer or needle attached to a coil of wire that is moveably positioned within the field of a permanent magnet.
Signals representative of a navigational parameter of the aircraft such as the position, heading, or glide slope of the aircraft are delivered to the coil. The signals set up a magnetic field around the coil and cause a torque to appear between the magnetic field of the magnet and the magnetic field of the coil. The torque moves the needle a distance proportional to the navigation signals to indicate the position, heading, glide slope or other navigational parameter of the aircraft.
Unfortunately, these prior art displays are extremely sensitive to contaminates because their magnets attract metallic and magnetic debris. The attracted contaminants interfere with the movement of the needles of the displays and therefore often cause erratic performance of the displays.
Contaminates can often completely prevent movement of the needles of D'Arsonval type displays because these types of displays generate very low torque to drive their needles. Thus, the displays and the aircraft in which the displays are used must be kept extremely clean to prevent malfunction of the displays.
Another disadvantage of D'Arsonval type displays is that since their needles are driven at such a low torque, they are very fragile and must be precisely aligned to maintain proper mechanical clearances between their moving coils, needles and surrounding mechanical structures. Thus, these displays must be precisely adjusted and maintained.